1. Field of the Invention
This invention relates to a tool for cutting a circular opening in a workpiece and maintaining control of the cut portion after cutting the circular opening.
2. Description of the Related Art
Circular openings and large holes are often needed in various workpieces, such as walls, plates, piping, and containers. A large drill bit could be used to cut the circular opening. However, large drill bits can be expensive and heavy. Also, it can be difficult to control the lateral location precision when using a large drill bit in a hand-stabilized drilling tool, such as an electric-powered hand drill. As an alternative to large drill bits, hole-saws are often used. Furthermore, using a drill bit to create a circular opening uses much more energy and requires a greater amount of torque and force since it cuts most all of the area corresponding to the circular opening, whereas a hole-saw cuts much less area (mainly the outer diameter of the circular opening) to create the same size hole.
Hole-saws currently exist in many configurations and designs. A hole-saw typically has a cylindrical shaped blade comprising cutting bits (e.g., saw teeth, hard grit particles) located circumferentially around its edge corresponding to the diameter of the desired circular opening. Hole-saws often have pilot shafts to enable the tool operator to align the center-point of the hole-saw blade with the desired center-point of the circular opening. The hole-saw pilot shaft can be inserted into a pilot hole corresponding to the center-point of the desired circular opening to stabilize the lateral location of the hole-saw blade and to create a more precise and cleaner circular opening cut. A pilot hole can be created, for example, using a separate tool (e.g., metal drill bit, wood auger, hole punch), or by the hole-saw's pilot shaft itself when the tip of the pilot shaft penetrates to form an opening
Hole-saws often come in kits having interchangeable hole-saw blade diameters that fit on a common drill arbor, where the drill arbor has a pilot shaft extending from it along the rotational axis and within the center of the hole-saw blade. The range of holesaw diameters in a kit is often in increments of standard sizes corresponding to the standard piping and conduit sizes for which the circular openings are often needed (e.g., plumbing, electrical wiring conduit routing).
Another alternative for cutting large circular openings is a circle cutter. A circle cutter typically has a single cutting bit or blade that rotates about a pilot shaft at a radius corresponding to the desired circular opening. The cutting bit is often removable and interchangeable for replacing worn bits or substituting a different bit type corresponding to the workpiece material. A circle cutter almost universally has an adjustable radial position for the single bit, which allows the same blade to cut a wide range of circular opening diameters. When using a hand-held drilling tool, it is essential for a circle cutter to have a pilot shaft. Much like the hole-saw, a circle cutter's pilot shaft can either be inserted into an existing hole created by a separate tool, or the pilot shaft itself can create the hole with its tip having a means for creating a pilot hole. When a circle cutter is held in a fixed machine while cutting the circular opening (e.g., end mill, lathe), the pilot shaft may not be as essential because the machine may provide enough stability for lateral location precision and alignment of the circle cutter.
Both hole-saws and circle cutters are often adapted to allow adjustable pilot shaft lengths. A longer pilot shaft may be easier to use because it can slide into the pilot hole and completely through the workpiece while providing the tool operator time during insertion to stabilize and ensure that the rotational axis of the hole-saw blade or circle cutter bit is normal to the workpiece. But, sometimes physical restrictions on the inside of the workpiece prevent the use of a longer pilot shaft that extends deep within workpiece while cutting the circular opening, which would make a short pilot shaft of a particular length more applicable. Hole-saws and circle cutters can also have interchangeable pilot shafts to allow the insertion of a variety of pilot shaft lengths and pilot shaft types (e.g., cutting thread tip, point tip, auger tip) to correspond to an array of workpiece physical restrictions and materials.
One of the major problems with existing hole-saws and circle cutters is that after the circular opening is cut, the cut portion is not controlled. Because the pilot shaft of conventional hole-saws and circle cutters can slide in and out of the pilot hole with or without pilot shaft rotation after a pilot hole is formed, the cut portion can freely slide off of the end of the pilot shaft. There are many applications where it is critical to maintain control of the cut portion to prevent it from falling into unwanted places where it can cause damage to things that it lands on or where it cannot be retrieved easily.
One example where it is critical to maintain control of the cut portion is during a wet-tapping or "hot-tapping" procedure on piping within a semiconductor wafer fabrication facility. Wet-tapping allows a new pipe to be connected into an existing pipe while the existing pipe still contains fluid under pressure. During a wet-tapping procedure, a circular opening is cut into the side of the existing pressurized pipe. Because fluid may be flowing within the pipe, there is a risk that the section of pipe removed (i.e., portion cut by the hole-saw) will fall into the pipe, or be pulled into the pipe by the fluid flow, and be carried downstream where it can create blockage or system damage. Downtime and damage to semiconductor wafer fabrication equipment is very costly and should be avoided whenever possible. Hence, there is a need to safely perform wet-tapping into piping without risk of collateral damage to the manufacturing systems. A need therefore exist for maintaining control of the cut portion after cutting a circular opening.